Post #59,237
10/24/02 7:35:34 PM
|
Dunno where to put this - graphic compression
I need to take a series of TIF
files that are multi-page faxes.
I need to convert them to some
other format so save space.
It is OK to lose image quality.
If possible, I'd like to join
them together into a single multi-page
viewable file.
I was under the impression that FAX TIF
files are already highly compressed.
But I guess it can get better if I'm
willing to lose quality.
I've played with the convert and mogrify
utilities that come with ImageMagic,
but don't know what to use (or the
right way) to get them smaller.
Any pointers?
|
Post #59,239
10/24/02 7:43:42 PM
|
jpegs are lossy
and you can save them specifying the level of loss you want..
I use gimp for this - I just change the scale of the image (usually so that it's 800 wide).
Hope This Helps!
Imric's Tips for Living- Paranoia Is a Survival Trait
- Pessimists are never disappointed - but sometimes, if they are very lucky, they can be pleasantly surprised...
- Even though everyone is out to get you, it doesn't matter unless you let them win.
|
Post #59,254
10/24/02 8:40:28 PM
|
jpegs don't *have* to be lossy
But I don't know how well the 0% loss jpeg stacks up against PNG.
|
Post #59,264
10/24/02 9:10:21 PM
|
Yup I know
I took the following
210147 a.tif
and did:
mogrify -scale 600x1200 -format jpeg *.tif
34815 a.jpeg.0
51699 a.jpeg.1
56333 a.jpeg.2
56718 a.jpeg.3
This cut the picture down to less than
1/4 the original size, and seems the limit
on viewable.
Which means I only save about 20%.
Can I do any better?
|
Post #59,245
10/24/02 8:03:14 PM
|
PNG or JPEG
PNG is not lossy, I believe.
An appropriate forum would have been General Q&A, for future reference.
Regards,
-scott anderson
"Welcome to Rivendell, Mr. Anderson..."
|
Post #59,269
10/24/02 9:16:37 PM
|
Thanks on the QA
I brainfarted.
|
Post #59,305
10/24/02 11:32:05 PM
|
More to the point (follow the line...)
...JPEG compression works by identifying regions of similar shading or color, and averaging large blocks together. PNG/GIF tends to be more vector oriented, and maps lines. \r\n\r\n Result: JPEG works pretty well for images and paintings (blobs of color). PNG/GIF works better for line drawings and text, uses where JPEG tends to produce "edge jitter". --\r\nKarsten M. Self [link|mailto:kmself@ix.netcom.com|kmself@ix.netcom.com]\r\n[link|http://kmself.home.netcom.com/|http://kmself.home.netcom.com/]\r\n
What part of "gestalt" don't you understand?\r\n
[link|http://twiki.iwethey.org/twiki/bin/view/Main/|TWikIWETHEY] -- an experiment in collective intelligence. Stupidity. Whatever.\r\n
\r\n
Keep software free. Oppose the CBDTPA. Kill S.2048 dead.\r\n[link|http://www.eff.org/alerts/20020322_eff_cbdtpa_alert.html|http://www.eff.org/alerts/20020322_eff_cbdtpa_alert.html]\r\n
|
Post #59,682
10/26/02 10:31:36 PM
|
Faxes would be "bi-level" images, and the best
compression results would come from [link|http://www.cl.cam.ac.uk/~mgk25/jbigkit/|JBIG] (Joint Bi-level Image experts Group) standards group. * Close to state-of-the-art lossless compression ratio for high resolution bi-level images.
* Around 1.1 to 1.5 times better compression ratio on typical scanned documents compared to G4 fax compression (ITU-T T.6), which has been the best compression algorithm for scanned documents available prior to JBIG.
* Up to 30 times better compression of scanned images with dithered images compared to G4 fax compression.
* Around 2 times better compression on typical 300 dpi documents compared to 'gzip -9' on raw bitmaps.
* Around 3-4 times better compression than GIF on typical 300 dpi documents. etc. Alex
"I have a truly marvelous demonstration of this proposition which this margin is too narrow to contain. -- Pierre de Fermat (1601-1665)
|
Post #59,852
10/28/02 10:11:22 AM
|
I thought faxes support gray-scale?
--
We have only 2 things to worry about: That
things will never get back to normal, and that they already have.
|
Post #59,965
10/28/02 9:37:20 PM
|
No. Group 3/group 4 compression of a fax is bi-level.
Now, you can use it for [link|http://desktoppub.about.com/library/weekly/aa090600a.htm|halftone] images. But any given pixel is either black or white. Your eye and brain integrate the pixels over the local area to see grays. This is exactly what you have in a newspaper picture. On any given spot you either have or not have ink. The local ratio of black to white in an area gives you the effect of grays.
Pull out your magnifying glass and take a close look.
Alex
"I have a truly marvelous demonstration of this proposition which this margin is too narrow to contain. -- Pierre de Fermat (1601-1665)
|
